1. Field of the Invention
Embodiments of the present invention relate to a wheel drive system for aircraft for rotating a wheel of an aircraft.
2. Description of the Related Art
Conventionally, an aircraft utilizes the power of an engine for flight for movement in an airport (taxiing). Generally, a moving speed obtained by such power is greater than a moving speed for safe taxiing, and taxiing is done while braking by a brake. Thus, consumption of fuel and wear of a brake by taxiing has been questioned. For the purpose of suppressing these problems, a proposal such as Patent Literature JP-T-2013-514229 below has been made. The proposal includes a motor for rotating a wheel of an aircraft, enables taxiing by rotating the wheel by the motor without using an engine for an aircraft, and suppresses consumption of energy and wear of a brake during taxiing.
Generally, a wheel of an aircraft stops rotation immediately before touchdown, and rotates suddenly by the friction with a runway immediately after touchdown. Then, the wheel is braked by a brake, and it is possible to slow down a whole aircraft by cooperating with other braking means such as an air brake. However, a severe friction occurs between the wheel and the runway during touchdown, and the wheel surface is greatly worn. For the purpose of reducing such wear, a proposal such as Patent Literature JP-A-2007-112408 has also been made. The proposal includes a motor for rotating a wheel prior to landing (pre-rotation), relieves the impact at touchdown, and suppresses the wear of a wheel by rotating the wheel to meet a relative speed of a runway.
A taxiing speed of an aircraft described above is relatively slow, approximately 35 km/h, and a large torque is required to move a heavy aircraft. Thus, a motor is required to have a low-speed high-torque output characteristic for rotating a wheel for taxiing.
On the other hand, a touchdown speed of an aircraft upon landing is relatively fast, 350 km/h or faster. It is sufficient to rotate only a wheel in pre-rotation. Thus, a motor is required to have a high-speed low-torque output characteristic for pre-rotation.
Taxiing and pre-rotation are both technologies utilizing a motor, but a required output characteristic is different. Thus, it is difficult to use a common motor to achieve both taxiing and pre-rotation.
In particular, when pre-rotation is performed by using a motor for taxiing, a high-speed rotation of about 10 times faster than taxiing is required, and a voltage of about 10 times greater than taxiing is required. Thus, when a wheel drive system is optimized according to a required voltage of a motor for taxiing, a withstand voltage of an electronic device such as an inverter provided in a voltage supply means exceeds an allowable value during pre-rotation. Contrarily, when a wheel drive system is optimized to meet a required voltage of a motor for pre-rotation, characteristics of an electronic device provided in a voltage supply means exceed those for taxiing, and production costs may extremely increase.